Multirange coupling circuit



w. D. LOUGHLIN ET AL MULTIRANGE COUPLING CIRCUIT Original Filed Sept. 4, 1950 waw 2 Sheets-Sheet l gwomtou:

Oct. 23, 1934. w, b. LOUG'HLIN ET AL 1,973,212

MULTIRANGE COUPLING CIRCUIT Original Filed sept. 4. 1950 2 Sheets-Sheet 2 ,ZZ AWZM QN .MJW

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Patented Oct. 23, 1934 UNITED STATES f MULTIRANGE COUPLING CIRCUIT William D. Lcughlin, Mountain Lakes, and Christopher J. Franks, Boonton, N. J assignors, by mesne assignments, to Radio Corporationof America, New York, N. Y., a corporation of Delaware Application September 4, 1930, Serial No. 479,728

Claims. (01. 178-44) This invention relatesto multirange coupling circuits and particularly to tuned circuits adapted to maintain efficient operation of vacuum tube amplifiers when tuned over a plurality of ranges of signal frequencies.

To obtain the desired sensitivity, selectivity and gain characteristics in a vacuum tube amplifier that is to be operated over an extended range of frequencies it has been customary to employ a series of interchangeable inductances or capacities. Tapped impedances and switches have been considered unsatisfactory dueto the wide variations in the performance of the arm plifier when operated at different frequency While better operating characteristics may be obtained with plug-in reactances, the

changing of the elements renders this method unsuitable for many purposes, such as for example, in broadcast receivers employing a plu- 20 rality of tuned amplifier stages. I

An, object ofthe present invention is to pro vide tuned coupling circuits including switches for changing the frequency band, which circuits exhibit satisfactory transmission characteristics for all frequency bands over which they may be tuned. A further object is to provide coupling circuits of the type stated which are particularly adapted for use as interstage couplings in cascaded amplifiers.

These and other objects will be apparent from the following specification, when taken with the .The input circuit for the first tube 1 takes the form of two substantially identical tuned circuits, each circuit including a high frequency inductance l, a loading inductance 5 and a tuning condenser 6. The tuned circuits are coupled by a common shunt impedance which preferably takes the form of a parallel circuit comprising a capacity 7 and an inductance 8. A series coupling capacity 9 is preferably provided between the high potential ends of the high frequency inductances 4, and this coupling may, and preferably is, obtained by a proper choice of the in cidental capacitive coupling between the tuned circuits. The junction of the tuning condensers is grounded, and the high potential terminals of the inductances 4 are connected to the antenna or other collecting structure 10 through a small coupling condenser 11, and to the control grid G1 of tube 1, respectively.

The inductances 4 and 5 of each circuit are shielded from each'other by mounting the same in separate shields, or within a single shield by arranging the coils at right angles to reduce the magnetic coupling substantially to zero. Switches 12 are provided for shortcircuiting the loading inductances 5 when it is desired to receive signals Within the higher range of frequen cles. r r

The tuned input circuit for the second tube Z includes a high frequency inductance 4, a loading inductance 5 and tuning condenser 6 which elements may be, and preferably are, identical with the corresponding elements of one of the tuned circuits associated with the tube 1. Due to the fact'that this tuned circuit is energized by the alternating voltage established in the plate 'cir cuit of tube 1, it will be apparent to one familiar withthe operation of vacuum tube amplifiers that the customarymethods of coupling to the platecircuit will not give satisfactory operation over both ranges of frequencies. When screen grid tubes of the tetrode or pentode type are employed, and theinvention is well adaptedfor use with such tubes, it is impractical to couple the plate of tube 1 to the control grid of tube 2 through a blocking condenser and to'supply the direct current potential to the plate P through a choke or resistance. r

The interstage coupling to the double range tuned circuit includes separate couplings to the high frequency inductance 4 and to the loading As shown in Fig. 1, the plate cirinductance 5. cuit of tube 1 includes a coil 13 which is coupled to the high frequency inductance 4 of the tuned circuit. The direct current circuit to plate P is range of frequencies this connection of the plate circuit to an intermediate point in the loading inductance 5 results in an autotransformer action that provides the desired degree of coupling between the plate circuit and the loading inductance. This coupling is, of course, in such sense as to assist the magnetic coupling between coil 13 and the high frequency inductance 4. A switch 16 is provided for shortcircuiting the portion 5a of inductance 5 when switch 12 is closed for reception in the higher frequency band. The resistor 1'7 is connected in shunt with the inductance 5 so that it acts as a losser resistance when the set is operated in the low frequency range. The grid bias path is through coils 5 and 4. The resistance 17 introduces a broadening efiect in the low frequency range of the receiver, and is short circuited when the switches 16 and 12 are closed for operating the receiver in the high frequency range.

As shown diagrammatically, the coil 13 takes the form of a spiral or pancake winding to reduce the capacitive coupling between coil 13 and inductance 4 to a minimum. This feature is quite important since it would be difficult or impossible to employ a single condenser 6 for tuning over both ranges if the capacity between inductance 4 and the ground was relatively large. The elimination of the coupling between the plate cir cult and the loading inductance 5 is essential if a satisfactory gain characteristic is to be obtained in the high frequency range. Except for the provision of the switch 16, the leakage inductance in the loading inductance section of the tuned circuit would resonate with the inherent capacity of tube 1 within the high frequency range, thus destroying both gain and selectivity.

When high selectivity is desired, the coupling between two of the audions, may take the form of the two coupled tuned circuits that are above described as comprising the coupling system between the antenna 10 and the first amplifier 1. Such a coupling system is illustrated in Fig. 1 in connection with the audions 2 and 3. Each of the tuned circuits and the couplings between the same may be, and preferably are, substantially identical with corresponding elements of the input system of the first audion. The coupling between the plate circuit of tube 2 and the first tuned circuit conforms, however, to the coupling between the plate of tube 1 and the tuned input circuit of the tube 2. Detailed description of the circuit elements is believed to be unnecessary as like elements are identified by the same reference numerals as those identifying similar elements of the input systems of tubes 1 and 2.

All of the tuning condensers 6 are connected in the usual manner by an appropriate mechanical connection 18 to insure the simultaneous tuning to resonance of all of the circuits. In practice, the condensers 6 preferably comprise the individual units of a gang condenser.

The coupling impedance between the tuned circuits of each pair is essentially capacitive, but the inductance 8 is preferably included in shunt with the coupling capacity '7 for two reasons. It provides a direct current path between ground and the control grid G1 of the next tube, thereby permitting the application of an appropriate bias Voltage on the grid. The inductance 8 has the further function of improving the fidelity of reception at the extreme low frequencies. By so choosing the value of inductance 8 that it resonates with capacity '7 at the low frequency end of the low frequency band, the impedance presented by the coupling unit increases as the frequency decreases and thereby increases the coupling between the circuits. This results in a broadening of the resonance curve for the lowest frequencies and thus reduces the cutting of the sidebands in this portion of the frequency spectrum.

One structural assembly of the coupling circuits which, in practice, has been found to be particularly eiiicient is illustrated in Figs. 2 and 3.

The inductance 4 has the form of a single layer winding upon tube 19 of insulating material that is supported, by brackets 20, upon one end and at right angles to a second tube 21 upon which the inductance 5 is wound. To reduce the size and distributed capacity of inductance 5, this winding is preferably bank-wound in a plurality of sections, as is shown in Fig. 3. The coupling inductance 13 is wound in a narrow slot at the edge of a disc 22 that is mounted within the tube 19, and centrally of the winding 4, by suitable means, such as drops 23 of cement.

The coupling condenser 15 and high frequency choke 14 are located within the tube 21 and, being of relatively light weight may be supported solely by the connecting leads. The axis of the choke 14 is at right angles to the axis of winding 5 to reduce the magnetic coupling substantially to zero.

As will be apparent from Fig. 3, this construction facilitates the assembly of the coupling units in a radio receiver by reducing the number of connections to be made to each unit. One end of the winding 4 is brought out to a terminal 24 on tube 19, and the opposite end of winding 4 is connected by a lead 25 to the adjacent end of the inductance 5. The tube 19 carries a second terminal 26 that is connected to one end of the coupling inductance 13, the opposite end of the inductance being connected, by lead 27, to that terminal of the coupling condenser 15 to which the choke 14 is connected. The opposite condenser terminal is connected, by lead 28, to a terminal 29 that is carried by the lower end of the tube 21. The intermediate tap 30, on winding 5, is connected to the lead 28, as shown in Fig. 3, or it may be run directly to the terminal 29. The lower ends of the winding 5 and choke 14 are connected to terminals 31 and 32, respectively, that are mounted on tube 21 near its lower end. The tube 21 is provided with brackets 33 for securing the assembled unit to a base or panel.

The particular assembly shown in Figs. 2 and 3 is intended for use as an interstage coupling such as shown between tubes 1 and 2 of Fig. 1. By omitting the disc 22 with its winding 13, the choke 14 and coupling condenser 15, the assembled unit then consists of only the windings 4 and 5, and this form is used for both units of the input system and for the second unit of the coupled circuits employed as an interstage coupling.

The following data with reference to one par ticular assembly designed for use at a high frequency range of from 550 to 1500 kilocycles and a low frequency range of from 150 to 3'75 kilocycles, is given merely as an example of circuit constants which have been convenient for one embodiment of the invention.

Inductance 4:100 turns of #30 (American Wire Gauge) enamel wire close wound in a single layer on a 1.25 inch tube.

Inductance 5:375 turns, #30 double silk covered wire bank wound in six sections on 1.25 inch tube, tapped at 125 turns from lower end. Inductance of 3.1 millihenries.

Inductance 13:60 turns, #38 double silk covcred wire wound in slot inch wide and inch internal diameter. i i

Choke l4=small highfrequency choke having low distributed capacity and 10-15 millihenries inductance. i

While theinvention has been described as applied to a coupling system adapted to operate efficiently over two frequency ranges, it will be apparent that thegeneral method of design applies equally well'when three or more ranges are tobecovered. 1

We claim: 3 1 l i 1. In an electrical transmission system, a pair of oscillation circuits, means for resonating each circuit to a desired frequency, and a reactive coupling path common to said circuits and in series with the elements of each of the circuits, said reactive path being resonant to a frequency close to the lowest frequency to whicheach of said circuits is resonated.

2. man electrical transmission system, a pair of oscillation circuits, means for resonating each circuit to a vdesired'frequency, and a reactive coupling path common to said circuits, said reactive path being resonant to a frequency close to the lowest frequency to which each of said circuits is resonated and. comprising an antiresonant network.

3. In an electrical transmission system, a pair of oscillation circuits, means forre'sonating each circuit to a desiredfrequency,and areactive coupling path common'to said circuits andin series with the elements of each of the circuits, said reactive path comprising a condenser and inductance coil and being resonant to a frequency close to the lowest frequency to which each of said circuits isresonated. j

4. In an electrical transmission system, a pair of oscillation circuits, means for resonating each circuit to a desired frequency, and a reactive coupling path common to said circuits, said reactive path comprising a condenser in shunt with an inductance and being resonant to a frequency close to the lowest frequency towhich each of said circuits is resonated. I

5. In an electrical transmission system, a pair I of oscillation circuits, means for resonating each circuit to a desired frequency, areactive coupling pathcommon to said circuits and in series with the elements of each of the circuits, said reactive path being resonant to a frequency close to the lowest frequency to which each of said circuits is resonated, and each of said oscillation circuits including an inductance and variable condenser arranged to be series resonant to a desired frequency. i

6. In an electrical transmission system, a pair of oscillation circuits, means for resonating each circuit to a common desired frequency, and a reactive coupling path common to said circuits and in series with the elements of each of the circuits, said reactive path being resonant to a frequency close to the lowest frequency to which each of said circuits is resonated.

'7. In an electrical transmission system, a pair of oscillation circuits, means for simultaneously resonating each circuit to a common desired frequency, and a reactive coupling path common I to said circuits, said reactive path being resonant to a frequency close to the lowest frequency to which each of said circuits is resonated.

8. In an electrical transmission system, a pair of oscillation circuits, means for simultaneously resonating each circuit to a common desired frequency, and a reactive coupling path common to said circuits, said reactive path being resonant to a frequency close to the lowest frequency to which each of said circuits is resonated and comprising an anti-resonant network.

'9; In combination, in a radio receiver a source of modulated signal energyyanelectron discharge tube provided with input and output electrodes, a coupling network connectedbetween said source and tube input electrodes, said network comprising a path of series resonant circuits, means for-simultaneously and similarly adjusting said circuits to a common desired frequency and an anti-resonant path coupling said series resonant circuits, said path being resonantat a frequency near the lower limit of the frequency range to which said circuits may be adjusted.

10. In combination, in a radio receiver a source of modulated signalenergy, an electron discharge tube provided with input and output electrodes, a coupling network connected between said sourceand tube input electrodes, said network comprising a pair of series resonant circuits, means for simultaneously and similarly adjusting said circuits -to a common desired frequency and an anti-resonant path including a condenser in parallel with an inductance coupling said series resonantcircuits, said path being resonant at a frequency near the lower limit of the frequency range to which said circuits may be adjusted.

11. Incombination, in a radio' receiver a source of modulated signal energy, an electron discharge tube provided with input and output electrodes, a coupling network connected between said source and tube input electrodes, saidnetwork comprising a path of series resonant circuits, means for simultaneously and similarly adjusting said circuits to a common desired frequency and an anti-resonant path coupling said series resonant circuits, said path being resonant at a frequency near the lower limit of the frequency range to which said circuitsmay be adjusted, said source consisting of a signal energy collecting means, said collecting means being connected to an'intermediate point on one of said series resonant circuits.

12. In combination, in aradioreceiver a' source of modulated signal energy, an electron discharge tube provided with input and output electrodes, a coupling network connected between said source and tube input electrodes, said network comprising a path of series resonant circuits, means for simultaneously and similarly adjusting said circuits to a common desired frequency and an antiresonant path coupling said series resonant circuits, said path being resonant at a frequency near the lower limit of the frequency range to which said circuits may be adjusted, said tube consisting of a screen grid tube the input electrodes thereof being connected between two points of one of said circuits having a radio frequency potential difference.

.13. In combination, in a radio receiver a source of modulated signal energy, an electron discharge tube provided with input and output electrodes, a coupling network connected between said source and tube input electrodes, said network comprising a path of series resonant circuits, means for simultaneously and similarly adjusting said circuits to a common desired frequency and an antiresonant path coupling said series resonant circuits, said path being resonant at a frequency near the lower limit of the frequency range to which said circuits may be adjusted, and. a condenser connecting two points of said circuits at a high radio frequency potential.

14. In combination, in a radio receiver a source of modulated signal energy, an electron discharge tube provided with input and output electrodes, a coupling network connected between said source and tube input electrodes, said network comprising a path of series resonant circuits, means for simultaneously and similarly adjusting said circuits to a common desired frequency and an antiresonant path coupling said series resonant circuits, said path being resonant at a frequency near the lower limit of the frequency range to which said circuits may be adjusted, a second tube coupled to the output electrodes of said first tube and means for adjusting the input circuit of the said second tube to said common frequency simultaneously with adjustment of said series resonant circuits.

15. In an electrical transmission system, a pair of oscillation circuits, means for resonating each circuit to a desired frequency, and a reactive coupling path common to said circuits, said reactive path being resonant to a frequency close to the lowest frequency to which each of said circuits is resonated and a condenser connecting two points of said oscillation circuits of high potential.

16. In combination, in a radio receiver a source of modulated signal energy, an electron discharge tube provided with input and output electrodes, a coupling network connected between said source and, tube input electrodes, said network comprising a path of series resonant circuits, means for simultaneously and similarly adjusting said circuits to a common desired frequency and an anti-resonant path coupling said series resonant circuits, said path being resonant at a frequency near the lower limit of the frequency range to which said circuits may be adjusted, each of said circuits comprising a pair of inductance coils in series with a variable condenser and means for short-circuiting one of the coilsito vary the frequency range of said circuits.

17. In combination in an electrical network, a pair of series resonant oscillation circuits, means for tuning the circuits through a desired frequency range, an impedance, common to said circuits, including capacity and inductance, said impedance being in series with the elements of each of said circuits and being resonant at a frequency at the low frequency limit of said range.

18. In combination, in a radio receiver a source of modulated signal energy, an electron discharge tube provided with input. and output electrodes, a coupling network connected between said source and tube input electrodes, said network comprising a path of series resonant circuits, means for simultaneously and similarly adjusting said circuits to a common desired frequency and an antiresonant path coupling said series resonant circuits, said path being resonant at a frequency near one limit of the frequency range to which said circuits may be adjusted, each of said circuits comprising a pair of inductance coils in series with a variable condenser and means for short-circuiting one of the coils to vary the frequency range of said circuits.

19. In combination, in a radio receiver a source of modulated signal energy, an electron discharge tube provided with input and output electrodes, a coupling network connected between said source and tube input electrodes, said network comprising a path of series resonant circuits, means for simultaneously and similarly adjusting said circuits to a common desired frequency and an antireson'ant path coupling said series resonant circuits, said path being resonant at a frequency near the lower limit of the frequency range to which said circuits may be adjusted, and said source of energy consisting of an antenna.

20. In combination, in a radio receiver a source of modulated signal energy, an electron discharge tube provided with input and output electrodes, a coupling network connected between said source and tube input electrodes, said network comprising a path of series resonant circuits, means for simultaneously and similarly adjusting said circuits to a common desired frequency and an antiresonant path coupling said series resonant circuits, said path being resonant at a frequency near the lower limit of the frequency range to which said circuits may be adjusted, and a condenser connecting two points of said circuits at a high radio frequency potential, and said source of energy consisting of an antenna.

WILLIAM D. LOUGHLIN. CHRISTOPHER J. FRANKS. 

